Abstract : We consider allocation problems that arise in the context of service allocation in Clouds. More specifically, on the one part we assume that each Physical Machine denoted as PM is offering resources memory, CPU, disk, network. On the other part, we assume that each application in the IaaS Cloud comes as a set of services running as Virtual Machines VMs on top of the set of PMs. In turn, each service requires a given quantity of each resource on each machine where it runs memory footprint, CPU, disk, network. Moreover, there exists a Service Level Agreement SLA between the Cloud provider and the client that can be expressed as follows: the client requires a minimal number of service instances which must be alive at the end of the day, with a given reliability that can be converted into penalties paid by the provider. In this context, the goal for the Cloud provider is to find an allocation of VMs onto PMs so as to satisfy, at minimal cost, both capacity and reliability constraints for each service. In this paper, we propose a simple model for reliability constraints and we prove that it is possible to derive efficient heuristics.